Network expansion is motivated by the prospects of new applications requiring a much higher capacity than that required by today's applications and is facilitated by the abundance of data transport capacity (often called bandwidth) of the optical telecommunication medium. The realizable capacity of a telecommunication network is virtually unlimited. A network structure that enables virtually unlimited expansion while providing a high service quality is desirable and its introduction is overdue.
Current communication networks, however, are complex. For example, the current Internet is complex and inefficient, with limited scalability and service capabilities: scalability relates to the ability of a network to grow to handle increasing traffic and accommodate a greater number of nodes; service capabilities relate to the ability of a network to provide flexible intelligent services and quality guarantees of various types of service. The current Internet lacks the versatility required in a growing global multi-service network, and its structure prohibits its growth without tremendous complexity and expense. This is further complicated by the unduly complex protocols that are an accumulation of patchwork performed since the Internet's inception.
Advances in optical and electronic technology have eliminated the need for complex structures and complex controls of telecommunication networks. A versatile inexpensive network scaling to a capacity that is orders of magnitude higher than the capacity of the current Internet is now realizable using simple network structures. The limitations that have led to the complexity and inefficiency of the current data networks have now been traversed. Adopting a simple network structure would enable the construction of an economical wide-coverage high-capacity high-performance network and the introduction of advanced communication services.
Applicant's U.S. patent application Ser. No. 09/286,431 filed on Apr. 6, 1999 and titled “Self-Configuring Distributed Switch ”, discloses a wide-coverage network of a composite-star structure that greatly simplifies network routing and control while facilitating growth to very high capacities. The disclosed network is based on adaptive wavelength channel allocation in an optical-core comprising several core nodes. To simplify the control functions, the core nodes operate independently from each other. The network is fully meshed and the paths have adaptive capacities. A technique for overcoming optical-switching latency in such a composite-star structure is described in U.S. Pat. No. 6,486,983, titled “Agile Optical-Core Distributed Packet Switch”, issued to Beshai et al. on Nov. 26, 2002.
It is well known that fine switching granularity can reduce the number of hops in a network and, hence, increase network efficiency. On the other hand, it is also recognized that some applications are better served through channel switching. Therefore, it may be beneficial to provide a network of mixed granularity. Applicant's U.S. patent application Ser. No. 09/671,140 filed on Sep. 28, 2000 and titled “Multi-grained Network” describes a network which includes edge nodes interconnected by core nodes having distinctly different granularities. The edge nodes switch multi-rate data traffic. The core may include core nodes that switch fixed-size data blocks, core nodes that switch channels or bands of channels, and core nodes that switch entire links. A core node that provides fine granularity by time sharing—for example, by switching data blocks occupying short time slots—must have a low switching latency in order to enable efficient time-sharing of wavelength channels.
The networks disclosed in the aforementioned patent applications require that each edge node have a sufficient capacity to enable direct linkage to the core nodes. Traffic sources may then access the edge nodes directly.
With the advent of fast optical switching devices, it may be desirable to relax the requirement that each edge node be of high capacity so that edge nodes of widely-varying sizes may be used while still maintaining the precious property of a small number of hops from any traffic source to any traffic sink. This would require exploring new network structures.